25. Eriogonum exilifolium Reveal, Great Basin Naturalist. 27: 114, fig. 1. 1967.
Drop-leaf wild buckwheat
Herbs, matted, not scapose, 0.3-1 × 1-2 dm, glabrous, green. Stems spreading, usually with persistent leaf bases, up to 5 height of plant; caudex stems matted; aerial flowering stems mostly erect, slender, solid, not fistulose, 0.03-0.1 dm, glabrous or floccose or sparsely tomentose. Leaves basal, 1 per node but congested; petiole 0.5-1 cm, tomentose to floccose or glabrous; blade linear to linear-oblanceolate, (2-)3-6 × 0.1-0.3 cm, densely white-tomentose abaxially, less so or glabrous and green adaxially, margins revolute. Inflorescences cymose-umbellate, 1.5-3 × 1.5-3 cm; branches dichotomous, glabrous; bracts 3, semileaflike, usually triangular, 3-5 mm. Peduncles stout, 0.1-0.4 cm, glabrous. Involucres 1 per node, turbinate-campanulate, 2.5-3.5(-4.5) × 2-3 mm, glabrous except for cottony tomentum between teeth; teeth 5, erect, 0.3-0.5 mm. Flowers 2-3.5 mm; perianth white, glabrous; tepals connate proximal 1/ 1/ 3, monomorphic, oblanceolate to elliptic; stamens exserted, 3-4 mm; filaments sparsely pilose proximally. Achenes brown, 2.5-3.5 mm, glabrous.
Flowering Jun-Sep. Clay hills and flats or granitic sandy slopes, mixed grassland and sagebrush communities; 2200-2600 m; Colo., Wyo.
Eriogonum exilifolium is known only from Grand, Jackson, and Larimer counties, Colorado, and from Carbon and Albany counties, Wyoming. The drop-leaf wild buckwheat is a “species of concern” in Wyoming.